1. Technical Field
The present invention relates to cranes and crane structures, and more particularly to the mounting of crane structures on offshore drilling platforms and rigs such as jackup rigs and the like. Even more particularly, the present invention relates to a method and apparatus for the mounting of a crane upon a jackup rig or offshore structure.
2. General Background
In the drilling of offshore oil wells for oil and gas, one of the methods used is to provide a working platform that is jacked up above the surface of the water having three or more legs implanted upon the sea floor. The use of such rigs is known in the art and they are known by various terms such as "jackup rigs" due to the use of a jacking system which usually involves a rack and pinion mechanism to elevate the barge with respect to the legs. Generally the legs for such a jackup unit consist of, for example, a cylindrical elongated tubular member having along its longitudinal axis an external rack. This rack cooperates with a jacking structure providing a powered pinion gear which rotates and causes the rack upon the leg to linearly move with respect to the barge thus raising or lowering the rig barge structure as desired. A jack frame is provided with is structurally connected to the barge or deck portion of the jackup rig and the pinion gear and its associated rotational power is affixed to this frame which necessarily is quite strong structurally being reinforced with the necessary structural steel beams or the like in order to properly transfer the load from the leg through the jacking mechanism including the pinion gear and the jack frame to its point of support upon the barge or rig floor.
Because of the high loads being transferred from the barge or rig deck to the legs, the jacking structure including the frame, the pinion gear and the motors are quite strong structurally and would adequately support a crane with minimum reinforcement. At any rate, to structurally reinforce the jacking frame with the necessary beams, gusset plate, and the like in order to support a crane of a given weight would be no problem once the weight of the crane was known as well as the weights it would be lifting and like such parameters.
It would be desirable to mount the lift crane which is necessary for lifting items on a jackup rig above the jacking structure and surrounding the leg of the crane. In this manner, vital space on the deck would be left available for other uses while the space above the jacking structure which normally would be free of anything would be a location for the lift crane when following the teaching of the present invention.
Besides the space saving features of the present invention, the mounting of a lift crane above the jacking structure and surrounding the leg provides additional safety in that the leg itself acts as a structural support in the event of bearing failure with the crane tipping a short distance before the leg catches it.
3. General Discussion of the Present Invention
The present invention thus provides a method and apparatus for the mounting of a lift crane on a jackup barge, rig, or the like which thus saves valuable rig floor space as well as attaches the crane in a safe manner which prevents its catastrophic failure upon a failure of the main crane support bearing.
The present invention provides a method for the mounting of a lift crane on a jackup rig. A first static bearing race portion is affixed to the jackup rig atop one of the rig jacking structures and surrounding the telescoping leg associated therewith. A second movable bearing race portion is affixed to the static race portion with a plurality of ball bearings therebetween allowing the first and second bearing race portions to rotate with respect to one another. A crane structure is then supported on the upper race portion with the telescoping leg of the jackup rig passing through both bearing race portions, with the crane structure unencumbering vertical movement of the leg. Thus, it is an object of the present invention to provide a method and apparatus for the mounting of a lift crane on, for example, a jackup rig which saves valuable deck space on the jackup rig while adequately supporting the crane structure.
It is another object of the present invention to provide a method for mounting a crane upon a jackup leg which utilizes the telescoping leg portion of the rig to support the crane in the event of a bearing failure.
Another object of the present invention is to provide a lift crane for use with jackup rigs and offshore platforms which can be easily adapted to existing structures.
Another object of the present invention is to provide a lift crane for use with offshore structures such as jackup rigs, offshore platforms and the like which utilizes as its structural support a portion of the offshore platform in a way which allows a smooth rotational bearing to support the crane yet prevents catastrophic failure in the event of bearing failure by utilizing a portion of the offshore structure to hold the crane in the event a bearing fails.
Another object of the present invention is to provide a crane apparatus and method of saving the expense of a substantial construction portion of the crane pedestal foundation by utilizing existing rig support at the jacking structure.
A feature of the present invention is the elimination of unnecessary weight and expense normally associated with the crane pedestal foundation by using existing structural elements of the jackup rig.